MACHINERY LUBRICATION- INDIA SEPTEMBER-OCTOBER 2019 | Page 34

OIL ANALYSIS
When the samples arrived at the
laboratory for testing, a 90-milliliter
subsample was immediately removed
from the translucent container and
placed directly into a dark drawer to
match the standard practice. The
sample was not reheated prior to
storage. The 90-milliliter subsample
was retained in the drawer for seven
days from its date of sampling and then
tested. An MPC of 21 was reported.
Both the light-blocking and translucent
oil sample containers were staged on
the laboratory counter surface for a
16-day period prior to additional MPC
testing. In this amount of time, it would
be expected that varnish would settle
out of the oil. MPC measurements were
made for both samples prior to heating
to determine their as-found varnish
levels.
The
translucent
sample
experienced a substantial increase from
its initial 21 MPC measurements to a
new level of 39. The light-blocking bottle
increased its varnish load to an MPC of
26.
Both samples were then heated, as
specified by ASTM D7843, to return the
varnish bodies into the oil and then
retested after allowing storage periods
of three, seven and 14 days from the
reheating. The sample containers were
stored in a dark location between each
test to avoid additional stress to the oil
from any light source.
The translucent sample was found to
have an MPC of 38 at three days, 40 at
seven days and 41 at 14 days. The
sample
from
the
light-blocking
container had a test measurement
similar to the original 90-milliliter
control sample with a reported MPC of
22 after three days. It rose to 24 after
seven days and continued to increase to
26 after 14 days from the time of
heating.
32 | September - October 2019 |
ASTM’s Response
The research presented in this article was reviewed at a recent meeting of the ASTM
Committee D02.C0.01 Turbine Oil Monitoring, Problems and Systems. We thank Bryan
Johnson for bringing this matter to our attention. This is an example of a fluid user presenting
research that helps to improve the value of our standards. With efforts like this, we make our
standards better for all end users.
Sections 8.1 and 8.2 of D7843 discuss the requirement of protecting the sample from UV
light, which we know can cause precision errors. However, these sections do not discuss specif-
ically the potential harmful issues associated with fluorescent light. We already have an open
work group item within our committee directed toward improvements of ASTM D7843 and
have now added this research for potential modifications in the next standard revision.
Modifications of ASTM standards are not made lightly. They require full ASTM D02 ballot
approval. Our objective is to recommend improved verbiage within the standard to reflect this
user’s input and its impact on precision so that future users can gain from this experience.
As you use ASTM standards in your business, keep in mind that we are always looking to
improve the precision and value of our standards. Become involved and be a part of this
improvement effort! – Dave Wooton, D02.C0.01 Committee Chairman
Both the light-blocking and translucent
oil sample containers were then
reheated a second time and stored in a
dark location for an additional seven
days. Retesting the sample from the
translucent container produced an
MPC of 40, while the sample from the
light-blocking container was measured
at 27.
Conclusions
The following conclusions were drawn
from this experiment. The comparison
of test data from the translucent and
light-blocking
sample
containers
supports observations that light
exposure can significantly impact MPC
test results. In this case, the light
exposure from the lab’s fluorescent
lighting permanently doubled the test
measurement within approximately two
weeks.
Allowing the sample to remain at
laboratory
temperatures
for
a
progressively longer time period
resulted in moderate increases in test
data. The variation in MPC test
measurements for the light-blocking
www.machinerylubricationindia.com
sample between a three- and seven-day
period was less than 10 percent (22 to
24). Either time interval could be
expected to produce acceptable trend
data provided a single interval is used
consistently. The results of the second
reheating test also showed an increase
for the light-blocking sample. This
suggests an oil sample should be tested
for MPC as soon as practical following
its removal.
While light exposure can be managed
by creating a subsample of the original
sample taken in the field, which can
then be separated and placed into a
dark storage location, this alternative
still affords the opportunity for the
sample to be inadvertently left in a
location with light exposure prior to
being turned over to the lab for testing.
In addition, the sample container may
be exposed to laboratory light as it is
processed, handled and tested. To
avoid the possibility of poor handling
practices for samples requiring an MPC
varnish test, it is recommended that
light-blocking sample bottles be used.